1. Field of the Invention
The present disclosure relates to a phase error detector used in Phase Locked Loop (PLL) circuit, and an optical disc device that detects address and records, using a generated clock.
2. Description of the Related Art
In recent years, recording density of an optical disc goes on increasing. In a field of video technology, optical discs such as a Digital Versatile Disc (DVD) and a Blu-ray (registered trademark) Disc (BD) and the like are well known. These optical discs are used as media for recording video data and also used as external storage media of personal computers. Meanwhile, as external storage media for personal computers, hard disks, flash memories and the like are also used. Compared with such media, the optical disc media have advantages of long life, high reliability, and no power necessity for retaining data.
In view of the advantages, optical disc media attract attention as archive media for storing important data, which is managed by data centers and the like. However, even an optical disc BD-XL which is one of the optical discs having the largest storage capacity, has a storage capacity of 128 GB per one disc. Therefore optical discs are required to store significantly larger space than other external media. Accordingly, it is required to further increase recording density of optical media.
There is a technology of land-and-groove recording which ensures high recording density of optical medium. An optical disc has a guide groove called groove provided for allowing precise control of a light spot to be positioned on a recording track. The technology of land-and-groove recording is for recording user data not only on a groove, but also on a so-called land formed between areas at which the groove is formed. As an optical disc using the technology of land-and-groove recording, DVD-RAM is well known.
Moreover, the optical disc is recorded a physical address associated with its location for recognition of the location to/from which user data is recorded/reproduced. There is a method that uses pre-pits used in the DVD-RAM for forming the physical address. However, since user data cannot be recorded on a portion where the pre-pits are formed, a recording capacity decreases.
In addition, as another method for forming the physical address, there is method which uses a meandering of a track (hereinafter referred to as wobble) and a wobble address is recorded on a wobble. The method which uses wobbles permits detection of the wobble address by a method different from a method of reproducing user data, and thus the recording capacity does not decrease.
In the method using the wobble address, a PLL is used for a reproduction signal of the wobble to generate a clock when data is recorded on the optical disc. The PLL has a phase error detector that detects a phase error, which is a difference between a phase of the reproduction signal of the wobble and a phase of the generated recording clock. The PLL controls the phase of the recording clock to bring the phase error close to zero.
Patent Literature 1 discloses a method for generating a recording clock based on a wobble signal. When the recording clock is generated based on the wobble signal, variation of linear velocity is incurred by eccentricity, motor variation or the like, which causes a residual in the PLL, so that the phase error may be disabled to be sufficiently brought close to zero. In this case, the above-described situation hinders the recording at a precise position on the optical disc. While increasing a loop gain of the PLL can reduce the residuals, the increase in loop gain is accompanied by an increase of an analog circuit such as an increase in a current of a charge pump used in the PLL and the like.